Aims. In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against
Introduction.
We analysed 54 alumina ceramic-on-ceramic bearings
from total hip replacements retrieved at one centre after a mean
duration of 3.5 years (0.2 to 10.6) in situ. These
implants were obtained from 54 patients (16 men and 38 women) with
a mean age of 67 years (33 to 88) who underwent revision for a variety
of reasons. Posterior
Non-optimal clinical alignment of components in total hip replacements (THRs) may lead to
Variations in component positioning of total hip replacements can lead to
Introduction and Aims. Clinically many factors such as variations in surgical positioning, and patients' anatomy and biomechanics can affect the occurrence and severity of
Introduction. Variations in component position can lead to dynamic separation and
Introduction.
Introduction and Aims. There are many variables that can affect the occurrence and severity of
Introduction and Aims. There are many surgical, implant design and patient factors that should be considered in preclinical testing of hip replacement which are not being considered in current standards. The aim of this study was to develop a preclinical testing method that consider surgical positioning, implant design and patient factors and predict the occurrence and severity of
Background. It is not always clear why some patients experience recurrent dislocation following total hip arthroplasty (THA). In order to plan appropriate revision surgery for such patients, however, it is important to understand the specific biomechanical basis for the dislocation. We have developed a novel method to analyse the biomechanical profile of the THA, specifically to identify
Introduction.
Introduction. Increased wear rates [1, 2] and acetabular rim fracture [3] of hip replacement bearings reported clinically have been associated with
Introduction. Total ankle replacement (TAR) is less successful than other joint replacements with a 77% survivorship at 10 years. Predominant indications for revision include: Insert dislocation, soft tissue impingement and pain/stiffness. Insert edge-loading may be both a product and cause of these indications and was reported to affect 22% of patients with the, now withdrawn from market, Ankle Evolutive System (AES) TAR (Transysteme, Nimes, France). Compressive forces up to seven times body weight over a relatively small contact area (∼6.0 to 9.2 cm. 2. ), in combination with multi-directional motion potentially causes significant polyethylene wear and deformation in mobile-bearing TAR designs. Direct methods of measuring component volume (e.g. pycnometer) use Archimedes' principle but cannot identify spatial changes in volume or form indicative of wear/deformation. Quantitative methods for surface analysis bridge this limitation and may advance methods for analysing the
Purpose of the study: Ceramic-on-ceramic THA explants exhibit a higher wear rate than that predicted by classical simulators. This appears to be related to
SUMMARY. The relationship between component position, wear rate and
Introduction:. A disturbing prevalence of painful inflammatory reactions has been reported in metal-on-metal (MoM) hip resurfacing arthroplasty. A contributing factor is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear include adverse cup orientation leading to proximity (<10 mm) of the hip reaction force to the edge of the acetabular component. As this phenomenon is a function of implant positioning and patient posture, this study was performed to investigate the occurrence of
Introduction. Robotically-assisted unicondylar knee arthroplasty (UKA) is intended to improve the precision with which the components are implanted, but the impact of alignment using this technique on subsequent polyethylene surface damage has not been determined. Therefore, we examined retrieved ultra-high-molecular-weight polyethylene UKA tibial inserts from patients who had either robotic-assisted UKA or UKA performed using conventional manual techniques and compared differences in polyethylene damage with differences in implant component alignment between the two groups. We aimed to answer the following questions: (1) Does robotic guidance improve UKA component position compared to manually implanted UKA? (2) Is polyethylene damage or
Introduction. A disturbing prevalence of short-term failures of metal-on-metal (MoM) hip resurfacings has been reported by joint registries. These cases have been primarily due to painful inflammatory reactions and, in extreme cases, formation of pseudotumors within periarticular soft-tissues. The likely cause is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear of metal-on-metal arthroplasties are thought to include adverse cup orientation, patient posture, and the direction of hip loading. The purpose of this study was to investigate the role of different functional activities in
Aims. Retrospective review of a consecutive series of 1,168 total ankle replacements (TAR) performed at Wrightington, to analyse modes of failure and clinical outcomes following TAR failure. Methods. All patients undergoing TAR between November 1993 – June 2019 were collated (4–25 year follow-up; mean 13.7 years). 6 implants were used (300 STAR, 100 Buechal Pappas, 509 Mobility, 118 Zenith, 41 Salto and 100 Infinity). 5 surgeons, all trained in TAR, performed the surgery. Modes of failure were collated and clinical and radiological outcomes recorded for the revisional surgery following failure of the TAR. Results. 156 (13.4%) TARs failed (47STAR 15.6%, 16BP 16%, 77Mobility 15.1%, 6Salto 14.6%, 10Zenith 8.5% and 0Infinity 0%). Mean time to failure 5.8 years (0.1- 21.4 years). The 4 most common modes of failure were 44.9% aseptic loosening, 11.5% gutter pain, 10.9% infection and 10.3% recurrent
Ceramic-on-ceramic bearings provide a solution to the osteolysis seen with traditional metal-on-polyethylene bearings. Sporadic reports of ceramic breakage and squeaking concern some surgeons and this bearing combination can show in vivo signs of
INTRODUCTION. Squeaking after total hip replacement has been reported in up to 10% of patients. Some authors proposed that sound emissions from squeaking hips result from resonance of one or other or both of the metal parts and not the bearing surfaces. There is no reported in vitro study about the squeaking frequencies under lubricated regime. The goal of the study was to reproduce the squeaking in vitro under lubricated conditions, and to compare the in vitro frequencies to in vivo frequencies determined in a group of squeaking patients. The frequencies may help determining the responsible part of the noise. METHODS. Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident(r), Stryker(r)) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster(r)). In-vitro 3 alumina ceramic (Biolox Forte Ceramtec(r)) 32 mm diameter (Ceramconcept(r)) components were tested using a PROSIM(r) hip friction simulator. The cup was positioned with a 75° abduction angle in order to achieve
Introduction and Aims: The extremely low wear rates of third generation alumina-alumina bearings in traditional hip simulators are not reflected in vivo. Separation of the bearing during swing phase and
This study compared component wear rates and pre-revision blood metal ions levels in two groups of failed metal-on-metal hip arthroplasties: hip resurfacing and modular total hip replacement (THR). There was no significant difference in the median rate of linear wear between the groups for both acetabular (p = 0.4633) and femoral (p = 0.0872) components. There was also no significant difference in the median linear wear rates when failed hip resurfacing and modular THR hips of the same type (ASR and Birmingham hip resurfacing (BHR)) were compared. Unlike other studies of well-functioning hips, there was no significant difference in pre-revision blood metal ion levels between hip resurfacing and modular THR.
The functional pelvic tilt when standing and sitting forward of 7402 cases on the OPS, Optimized Ortho, Australia Data Base were reviewed. All patients had undergone lateral radiographs when standing simulating extension of the hip, and sitting forward when the hip is near full flexion. Pelvic tilt was measured as the angle of the Anterior Pelvic Plane to the vertical Sagittal Plane, rotation anteriorly being given a positive value. Pelvises that had rotated more than 13 degrees anteriorly (+ve) when sitting forward or posteriorly (-ve) when standing were considered to place the hip at increased risk of dislocation or
Mismatch of bearing component centres and tension of soft tissues surrounding the hip joint can lead to component separation during gait cycle and cause the femoral head to contact the rim of an acetabular liner, which could increase wear and shorten lifespan of an implant. This study aims to investigate the contact and wear mechanics of a metal-on-polyethylene hip joint under dynamic separation by using Finite Element Analysis (FEA). A Pinnacle® cup with a Marathon neutral liner 36×56mm with a 45° inclination was constrained by a spring element in the medial-lateral axis. The spring was pre-compressed by 4mm to represent the corresponding translational mismatch of a simulator testing. Archard's law was used to predict wear over one ISO 14242-1 gait cycle. Contact pressure is proportional to the load input during the stance phase, associated with concentric contact condition; it increases threefold just before the swing phase (time C), reaching 46.2MPa, where
Introduction: Squeaking after total hip replacement has been reported in up to 10% of patients. Some authors proposed that sound emissions from squeaking hips result from resonance of one or other or both of the metal parts and not the bearing surfaces. There is no reported in vitro study about the squeaking frequencies under lubricated regime. The goal of the study was to reproduce the squeaking in vitro under lubricated conditions, and to compare the in vitro frequencies to in vivo frequencies determined in a group of squeaking patients. The frequencies may help determining the responsible part of the noise. Methods: Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident. ®. , Stryker. ®. ) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster. ®. ). In-vitro 3 alumina ceramic (Biolox Forte Ceramtec. ®. ) 32 mm diameter (Ceramconcept. ®. ) components were tested using a PROSIM. ®. hip friction simulator. The cup was positioned with a 75° abduction angle in order to achieve
Malpositioning still occurs in total hip arthroplasty (THA). As a result of mal-orientation, THA bearing can be subjected to
Introduction. Two types of ceramic materials currently used in total hip replacements are third generation hot isostatic pressed (HIPed) alumina ceramic (commercially known as BIOLOX®forte, CeramTec) and fourth generation alumina matrix composite ceramic consisting of 75% alumina, 24% zirconia, and 1% mixed oxides (BIOLOX®delta, CeramTec). Delta ceramic hip components are being used worldwide, but very few studies have analyzed retrieved delta bearings. The aim of this study is to compare
In vitro the introduction of microseparation and
Introduction: Squeaking is reported ceramic-on-ceramic hip bearings in association with acetabular component malposition – particularly too much or too little anteversion. Acoustic analysis of squeaking hips with modular ceramic-titanium acetabular components suggests that there may be dynamic uncoupling of the ceramic insert from the titanium shell with
Introduction. Stripe wear, observed on retrieved ceramic hip replacements, has only been replicated in vitro under translational mal-positioning conditions where the centres of rotation of the head and the cup are mismatched. 1,2. ; an in vitro condition termed “microseparation”. The aim of this study was to compare the
Malorientation of the acetabular cup in Total Hip replacement (THR) may contribute to premature failure of the joint through instability (impingement, subluxation or dislocation), runaway wear in metal-metal bearings when the edge of the contact patch encroaches on the edge of the bearing surface, squeaking of ceramic-ceramic bearings and excess wear of polyethylene bearing surfaces leading to osteolysis. However as component malorientation often only occurs in functional positions it has been difficult to demonstrate and often is unremarkable on standard (usually supine) pelvic radiographs. The effects of spinal pathology as well as hip pathology can cause large rotations of the pelvis in the sagittal plane, again usually not recognized on standard pelvic views. While Posterior pelvic rotation with sitting increases the functional arc of the hip and is protective of a THR in regards to both
Hip impingement causes clinical problems for both the native hip, where labral or chondral damage can cause severe pain, and in the replaced hip, where subluxation can cause squeaking/metallosis through
Introduction and Aims. In order to improve the longevity and design of an implant, a wide range of pre-clinical testing conditions should be considered including variations in surgical delivery, and patients' anatomy and biomechanics. The aim of this research study was to determine the effect of the acetabular cup inclination angle with different levels of joint centre mismatch on the magnitude of dynamic microseparation, occurrence and severity of
INTRODUCTION. Retrieval and clinical studies of metal-on-metal (MoM) bearings have associated increased wear. 1. and elevated patient ion levels. 2. with steep cup inclination angles and
In total hip arthroplasty (THA), inappropriate cup alignment cause
Introduction. Translational surgical mismatch in the centres of rotation of the femoral head and acetabular cup in hip joint replacements can lead to dynamic microseparation resulting in
Background. High cup abduction angles generate increased contact stresses, higher wear rates and increased revision rates. However, there is no reported study about the influence of cup abduction on stresses under head lateralisation conditions for ceramic-on-Ceramic THA. Material and method. A finite elements model of a ceramic-on-ceramic THA was developed in order to predict the contact area and the contact pressure, first under an ideal regime and then under lateralised conditions. A 32 mm head diameter with a 30 microns radial clearance was used. The cup was positioned with a 0°anteversion angle and the abduction angle was varied from 45° to 90°. The medial-lateral lateralisation was varied from 0 to 500 microns. A load of 2500 N was applied through the head center. Results. For 45° abduction angle,
The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or
Squeaking in hip arthroplasty is now well-documented but hitherto poorly understood. In this paper, we report data progressively accumulated from a series of studies undertaken by our group to investigate the mechanisms of noise production associated with ceramic-on-ceramic bearings. We reviewed demographic and radiographic data comparing squeaking with silent hips.
The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or
Ceramic hip components are known for their superior material properties concerning the invivo loading situation. In comparison to other commonly used materials, ceramics have a very low friction coefficient and a high fracture load. However, there are a few reported occasions of in-vivo fracture of ceramic ball heads. An experimental set-up imitating the in-vivo loading situation is used to analyze different scenarios that may lead to the fracture of the ball heads, such as dynamic
Background. Pseudotumours have been associated with metal-on-metal (MoM) hip replacements. We define it as a solid mass which may have cystic components that is neither neoplastic nor infectious in aetiology. The cause of a pseudotumour is not fully understood but could be due to excessive wear, metal hypersensitivity or due to an as-yet unknown cause. Aim. We present the retrieval analysis of early failure MoM hips revised for pain, loosening or a symptomatic mass. Tissues and implants were examined for the possible causes of failure and pseudotumour formation. Corrosion as a potential new cause for pseudotumour formation will be presented. Methods. A group of 16 MoM hip replacements were collected for retrieval analysis. Six of which had a pseudotumour. An Artificial Hip Profiler (Redlux Ltd) was used to measure wear.
No, not my mother, but metal-on-metal (MoM) hips! My involvement in the DEFENSE side of MoM hips has allowed me the luxury of reflection and continued study on the basic and clinical science of this particular wear couple. Much of what I have learned is relevant to other articular couples, and might help you in your next THR. No amount of in vitro laboratory testing can replicate or predict in vivo behavior of a particular wear couple. (Mother Nature always has something new to teach us!) Although MoM implants went through complete pre-market evaluation and approval in both the US and EU, the process is inadequate and does not assure safety or success of new designs and materials. Two year results obtained in pre-market (IDE) studies are of insufficient follow-up for accurate evaluation of new materials or designs. Be conservative! Be neither the first, nor the last, to embrace new technology!. Clinical experience and retrieval analysis of MoM devices has revealed factors that are not as apparent for other wear couples such as metal-on-polyethylene (MoP), or ceramic-on-ceramic (CoC). For instance:. All THR's are at risk of micro-lateralization, or displacement of the femoral head from the acetabular wear couple during swing phase, resulting in
Purpose of the study: Implantation of the acetabular socket with high inclination generates increased contract stress, wear and revision rate for total hip arthroplasty (THA). Study of ceramic-on-ceramic THA explants has revealed a high wear rate in bands, suggesting a microseparation effect generating
Abstract. Objectives. Hip joint laxity after total hip arthroplasty (THA) has been considered to cause microseparation and lead to complications, including wear and dislocation. In the native hip, the hip capsular ligaments may tighten at the limits of range of hip motion and provide a passive stabilising force preventing
Background. In vivo fluoroscopic studies have proven that femoral head sliding and separation from within the acetabular cup during gait frequently occur for subjects implanted with a total hip arthroplasty. It is hypothesized that these atypical kinematic patterns are due to component malalignments that yield uncharacteristically higher forces on the hip joint that are not present in the native hip. This in vivo joint instability can lead to
Background. Extensive research has previously been conducted analyzing the biomechanical effects of rotational changes (i.e. version and inclination) of the acetabular cup. Many sources, citing diverse dislocation statistics, encourage surgeons to strive for various “safe zones” during the THA operation. However, minimal research has been conducted, especially under in vivo conditions, to assess the consequences of cup translational shifting (i.e. offsets, medial and superior reaming, etc.). While it is often the practice to medialize the acetabular cup intraoperatively, there is still a lack of information regarding the biomechanical consequences of such cup medializations and medial/superior malpositionings. Objective. Therefore, the objective of this study is to use a validated forward solution mathematical model to vary cup positioning in both the medial and superior directions to assess simulated in vivo kinematics. Methods. The model used for this study has been validated with telemetric data and incorporates numerous muscles and ligaments. The model is parametrically derived and allows the user to simulate a theoretical THA surgery and to assess the outcomes of proper positioning as well as malpositioning of the cup. Parameters of interest in this study are component positions, joint instability and sliding, and contact area. Results. An intraoperative representation of the pelvis and cup was assessed (Figure 1), with a green star showing the native anatomical center, the red circle showing the acetabular cup center, and the arrow representing the reaming direction. During swing phase, it was determined that unaccounted for acetabular cup shifting of 5–10 mm leads to capsular ligament laxity coupled with an increase in hip joint instability. Two swing phase scenarios were assessed, one simulating adequate capsular tension and therefore a uniform contact patch and the other simulating inadequate capsule tension and therefore femoral component pistoning with a smaller contact patch (Figure 2). During stance phase, it was determined that acetabular cup shifting of 5–10 mm in the medial and/or superior directions yields an increase in hip joint instability. Two stance phase scenarios were simulated, one yielding no hip separation and therefore a uniform, centralized contact patch, and the other yielding ∼1.5 mm of hip separation and therefore a non-uniform, supero-lateral
Introduction. All hip replacements depend upon good orientation and positioning to ensure that implants function well in vivo. Mal-orientated devices can lead to poor patient gait, poor range of motion, impingement,
INTRODUCTION. Ceramic-on-metal hip replacements (COM, where the head is a Biolox Delta ceramic and liner is Co Cr alloy), have demonstrated reduced wear under standard conditions in vitro compared to metal-on-metal (MOM) [1]. Early clinical results are also encouraging [2]. Recently concerns have been raised regarding the poor clinical performance of MOM hip resurfacings [3], particularly when cups are steeply inclined. Laboratory hip simulator testing has been used to replicate
Introduction: The goal of the study was to compare the squeaking frequencies of Ceramic-on-Ceramic THR in-vitro and in-vivo among patients who underwent THR. Method: Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident. ®. , Stryker. ®. ) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster. ®. ). In-vitro 2 alumina ceramic (Biolox Forte Ceramtec. ®. ) 32 mm diameter (Ceramconcept. ®. ) components were tested using a PROSIM. ®. hip friction simulator. The cup was positioned with a 70° abduction angle in order to achieve
Introduction.
Introduction. Because of concerns regarding excessive wear and short-term failures attributed to the metal-on-metal bearings, the use of metal-on-metal hip resurfacing arthroplasty (MOMHRA) has been greatly reduced since 2008, despite great mid-term results for well-designed implants and in certain patient populations. The true cause of excessive wear was then unknown. Therefore, identification of true risk factors for the procedure became paramount to refine indications and improve survivorship outcomes. Methods. Over the last 10 years, a systematic search of the US national library of Medicine and National institutes of health with the key words “metal-on-metal” and hip resurfacing” was conducted and returned 2186 items. Of these items, 862 were deemed relevant to our research purposes and entered in our center's reference database from which this review was performed. Results.
Introduction. Tribological studies have described a characteristic wear pattern of metal-on-metal hip resurfacings (MoMHRAs) with a run-in period followed by a ‘bedding-in’ phase minimising wear or by an increasing wear patch with
INTRODUCTION. Ceramic hip components are known for their superior material properties and longevity. In comparison to other materials commonly used, ceramics have a very low friction coefficient and a high fracture load. However, even though in-vivo fractures of ceramic ball heads are a relatively rare occurrence compared to other reasons for revision, they are of concern to the surgeon using ceramic components. The goal of this work was to evaluate the most probable causes for fracture and to quantify the influence of the metal taper contamination and shell deformation, respectively. METHODS. An experimental set-up imitating the in-vivo loading situation was used to analyze different scenarios that may lead to the fracture of the ball heads, such as dynamic
INTRODUCTION. Ceramic-on-ceramic hip replacements have generated great interest in recent years due to substantial improvements in manufacturing techniques and material properties. 1. Microseparation conditions that could occur due to several clinical factors such as head offset deficiency, medialised cup combined with laxity of soft tissue resulting in a translation malalignment, have been shown to cause
Introduction. Total ankle replacement (TAR) is surgically complex; malalignment can arise due to surgical technique or failure to correct natural varus/valgus malalignment. Across joint replacement, malalignment has been associated with pain, component
Introduction. Contemporary total knee systems accommodate for differential sizing between femoral and tibial components to allow surgeons to control soft tissue balancing and optimize rotation. One method some manufacturers use to allow differential sizing involves maintaining coronal articular congruency with a single radius of curvature throughout sizes while clipping the medial-lateral width, called a single coronal geometry system. Registry data show a 20% higher revision rate when the tibial component is smaller than the femur (downsizing) in the DePuy PFC system, a single coronal system, possibly from increased stresses from
Introduction. Successful cementless acetabular designs require sufficient initial stability between implant and bone (with interfacial motions <150 μm) and close opposition between the porous coating and the reamed bony surface of the acetabulum to obtaining bone ingrowth and secondary stability. While prior generations of cementless components showed good clinical results for long term fixation, modern designs continue to trend toward increased porosity and improved frictional characteristics to further enhance cup stability. Objectives. We intend to experimentally assess the differences in initial stability between a hemispherical acetabular component with a highly porous trabecular tantalum fixation surface (Continuum. ®. Acetabular System, Zimmer Inc, Warsaw, IN)(Fig 1) and a hemispherical component with the new highly porous Trabecular Titanium. ®. surface (Delta TT, Lima Corporate, Italy)(Fig 2) manufactured by electron beam melting. Material and methods. A total of 16 cups were used, 8 for each type. Each cup was used 4 times. Cups were implanted in polyurethane foam blocks with 1mm interference fit and subsequently edge loaded to failure. Two different foam block densities (0.24 g/cm. 3. and 0.32g/cm. 3. ) were used to model low- and high-density bone stock. Each cup was seated into a block under displacement control using a servohydraulic test machine (MTS Bionix 858, Eden Praire, MN) to engage the locking mechanism until axial forces reach 8 to 10 kN. During insertion, force and displacement were recorded to determine the implantation force for each component. After seating, initial acetabular component fixation was assessed using an
INTRODUCTION. Aseptic loosening is the most common failure mode for Total Elbow Arthroplasty (TEA) and is considered to be associated with accelerated polyethylene bearing wear [1, 2]. This study aimed to evaluate three commercially available implant designs under loads associated with daily living. The hypothesis was that more recent designs (Discovery and Nexel) provide greater articular contact areas resulting in lower polyethylene stresses compared to the Coonrad/Morrey (CM). METHODS. Motion tracking was performed on a healthy volunteer during elbow flexion at 0, 45, and 90° shoulder abduction because most daily activities occur with some shoulder abduction [3] resulting in varus stress about the elbow. This kinematic data was used in an OpenSim upper extremity musculoskeletal model [4] to estimate muscle and joint reaction loads with 5lb in hand, consistent with the common clinical restrictions following TEA. Computer aided assemblies of the smallest size implants for each system were imported to ANSYS for finite element analysis. Metallic components were treated as rigid and polyethylene components were modeled using a nonlinear elastoplastic constitutive model calibrated to material data. Articular contacts were frictional. Physiologic joint reaction forces and moments quantified in OpenSim were applied and the resulting peak articular contact area and peak bearing von Mises stresses were assessed. RESULTS. Simulated deformation patterns of CM bearings corresponded well to those reported in retrievals studies [1, 2] supporting the clinical relevance of the modeling approach. Peak stresses for CM and Nexel were consistently found in the central and side bearings respectively. The central bearing stresses remained 2–2.6 times lower in Nexel compared to CM. Peak stress for all three TEA systems increased with shoulder abduction (Fig.1, 2). Highest peak stresses (Fig.2) were obtained in CM and consistently exceeded the polyethylene yield limit; CM showed the lowest contact area (Fig.3). Nexel and Discovery experienced peak polyethylene stresses 26–34% and 17–39% lower than CM respectively (Fig.2). DISCUSSION. Our results support the hypothesis that newer TEA systems provide increased articular contact area and reduced bearing stresses during physiological loading. The cylindrical CM central bearing carries both the joint reaction force and moment leading to
Hip resurfacing using metal-on-metal bearings has a number of purported advantages over traditional total hip replacement in the young, active patient. Males in particular can benefit from the bone preservation, stability, and higher activity levels seen with this procedure. As more is learned about the factors affecting long-term outcome of hip resurfacing, component position has emerged as one major predictor of success. Given a well-selected patient, and a well-designed device, acetabular positioning is perhaps the most important determinant of long-term survivorship in hip resurfacing. One feature of resurfacing socket design which has not been widely disseminated is the sub-hemispheric arc of the bearing surface. While the outer circumference of the socket represents a complete hemisphere, and radiographic evaluation may assume that the apparent socket angle is satisfactory, the actual bearing is less than a hemisphere, so that the true abduction of the bearing is considerably more vertical. This important fact leads to excessive bearing inclination,
Large heads offer substantial advantages over small ones in hip arthroplasty, as they are far less likely to dislocate. This feature is of particular benefit in very dysplastic females who often have a degree of joint laxity making dislocation a real possibility. Large metal heads have a range of problems, so registries report that they are now being substituted by large ceramic heads, typically reducing in diameter by 15% or more from the native size. All current designs of the femoral ball heads, whether for resurfacing of replacement share a unique design characteristic: a subtended angle of 120° defining the proportion of a sphere that the head represents. A novel design has recently been proposed that might reduce conflict between the femoral ball head rim and the iliopsoas tendon. This paper explains the problem of iliopsoas impingement on femoral heads of native diameter, and the consequences. Material and Methods. Using MRI, we measured the contact area of the Iliopsoas tendon on the femoral head in sagittal reconstruction of 20 hips with symptoms of FAI. We also measured the Articular extent of the femoral head on 40 normal hips and 10 dysplastic hips. We then performed virtual hip resurfacing on normal and dysplastic type hips, attempting to avoid the overhang of the rim inferomedially. Results. The contact area of the Iliopsoas tendon on the femoral head in extension is well visualized (Figure 1). The femoral head articular surface has a subtended angle of 120° anteriorly and posteriorly, but only of 100° medially. Virtual surgery in a femoral head of a dysplastic hip showed that when the femoral head is resurfaced with an anatomic sized component, the femoral ball head has a 20° skirt of metal protruding medially where iliopsoas articulates (figure 2). Reducing this by 15%, (eg to put a 40mm ball head onto a hip that had a 46mm femoral diameter), completely avoids any chance of iliopsoas tendon using the femoral head as a fulcrum. MRI of a dysplastic hip with a 40mm ball shows that iliopsoas impingement is hard to substantiate (figure 3). Discussion. The excessive extent of the femoral components of anatomic proportions may contribute to the pain felt by many following their use. However, the 15% reduction in head size undertaken in total hip arthroplasty completely defunctions the femoral head as a fulcrum. Groin pain is a real issue following hip arthroplasty, but
The Articular Surface Replacement (ASR) hip resurfacing arthroplasty has a failure rate of 12.0% at five years, compared with 4.3% for the Birmingham Hip Resurfacing (BHR). We analysed 66 ASR and 64 BHR explanted metal-on-metal hip replacements with the aim of understanding their mechanisms of failure. We measured the linear wear rates of the acetabular and femoral components and analysed the clinical cause of failure, pre-revision blood metal ion levels and orientation of the acetabular component. There was no significant difference in metal ion levels (chromium, p = 0.82; cobalt, p = 0.40) or head wear rate (p = 0.14) between the two groups. The ASR had a significantly increased rate of wear of the acetabular component (p = 0.03) and a significantly increased occurrence of
Achieving optimal acetabular cup orientation in Total Hip Replacement (THR) remains one of the most difficult challenges in THR surgery (AAOR 2013) but very little has been added to useful understanding since Lewinnek published recommendations in 1978. This is largely due to difficulties of analysis in functional positions. The pelvis is not a static reference but rotates especially in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic rotation have a substantial effect on the functional orientation of the acetabulum, not appreciated on standard radiographs [Fig1]. Studies of groups of individuals have found the mean pelvic rotation in the sagittal plane is small but large individual variations commonly occur. Posterior rotation, with sitting, increases the functional arc of the hip and is protective of a THR in regards to both
We have performed an RCT of cross-linked versus non cross-linked polyethylene with 125 patients followed for five years. The study showed a dramatic reduction of wear with the cross-linked polyethylene consistent with the in-vitro studies. Because it has been recognised that hard bearings are sensitive to
Introduction. Ceramic composites have been developed to further improve the mechanical properties, reduce risk of fracture, and increase the survivorship of ceramic-on-ceramic bearings in total hip replacement. 1. . The aim of this study was to evaluate the wear of two novel ceramic composite materials under
Introduction: The purpose of this study was to determine the effects of
We studied 33 third generation, alumina ceramic-on-ceramic bearings retrieved from cementless total hip replacements after more than six months in situ. Wear volume was measured with a Roundtest machine, and acetabular orientation from the anteroposterior pelvic radiograph. The overall median early wear rate was 0.1 mm. 3. /yr for the femoral heads, and 0.04 mm. 3. /yr for the acetabular liners. We then excluded hips where the components had migrated. In this stable subgroup of 22 bearings, those with an acetabular anteversion of <
15° (seven femoral heads) had a median femoral head wear rate of 1.2 mm. 3. /yr, compared with 0 mm. 3. /yr for those with an anteversion of ≥15° (15 femoral heads, p <
0.001). Even under
Squeaking is a rare complication of hard-on-hard hip bearings. Occasionally the noise is troublesome enough to warrant revision surgery. The purpose of this study is to contribute to the understanding of the mechanism(s) underlying squeaking. We analyzed 10 alumina ceramic-on-ceramic bearings from squeaking hips collected at revision surgery. The reason for revision was given as squeaking (6 cases) or squeaking and pain (4 cases). Six of the 10 patients were male, average patient age was 48. Bearings were retrieved after an average of 23 months in service (11 to 61 months). There were 4 different designs of acetabular component from 2 different manufacturers. Nine have an elevated metal rim which is proud of the ceramic and one does not. Two bearings were 36mm in diameter, 6 were 32mm and 2 were 28mm. All 10 bearings showed evidence of
Introduction. Previous research defines the existence of a “safe zone” (SZ) pertaining to acetabular cup implantation during total hip arthroplasty (THA). It is believed that if the cup is implanted at 40°±10° inclination and 15°±10° anteversion, risk of dislocation is reduced. However, recent studies have documented that even when the acetabular cup is placed within the SZ, high incidence dislocation and instability remains due to the combination of patient-specific configuration, cup diameter, head size, and surgical approach. The SZ only investigates the angular orientation of the cup, ignoring translational location. Translational location of the cup can cause a mismatch between anatomical hip center and implanted cup center, which has not been widely explored. Objective. The objective of this study is to define a zone within which the implanted joint center can be altered with respect to the anatomical joint center but will not increase the likelihood of post-operative hip separation or dislocation. Methods. A theoretical forward solution hip model, previously validated by telemetric devices and fluoroscopy data of existing implants, was used for analysis. The model allows for modifications of implant geometries/placement and soft tissue resection to simulate various surgical conditions. For the baseline simulation, the cup center was matched to the anatomical hip joint center, calculated as the center of the best fit sphere mapping the acetabulum, and the orientation of the cup was 40°/15° (inclination/anteversion). Keeping cup orientation the same, the location of the cup was moved in 1 mm increments in all directions to identify the region where a mismatch between the two centers did not lead to separation or instability in the joint. Results. During both swing and stance phase, when the acetabular cup was placed within the optimal conic with a slant height of 5±1 mm, no hip instability or dislocation risk occurred. As the acetabular cup was translated to the boundary of the optimal conic, hip instability increased. When the acetabular cup was placed at the boundary of the optimal conic, up to 2 mm of hip separation in the lateral direction occurred during swing phase, resulting in a decrease in contact area and an increase in contact stress. As the cup was placed outside the optimal conic, severe
Pseudotumours are a rare complication of hip resurfacing. They are thought to be a response to metal debris which may be caused by
We investigated the characteristics of patients
who achieved Japanese-style deep flexion (seiza-sitting) after total knee
replacement (TKR) and measured three-dimensional positioning and
the contact positions of the femoral and tibial components. Seiza-sitting
was achieved after surgery by 23 patients (29 knees) of a series
of 463 TKRs in 341 patients. Pre-operatively most of these patients
were capable of seiza-sitting, had a lower body mass index and a favourable
attitude towards the Japanese lifestyle (27 of 29 knees). According
to two-/three-dimensional image registration analysis in the seiza-sitting
position, flexion, varus and internal rotation angles of the tibial
component relative to the femoral component had means of 148° (. sd. 8.0),
1.9° (. sd. 3.2) and 13.4° (. sd. 5.9), respectively.
Femoral surface contact positions tended to be close to the posterior
edge of the tibial polyethylene insert, particularly in the lateral
compartment, but only 8.3% (two of 24) of knees showed femoral subluxation
over the posterior edge. The mean contact positions of the femoral
cam on the tibial post were located 7.8 mm (. sd. 1.5) proximal
to the lowest point of the polyethylene surface and 5.5 mm (. sd. 0.9)
medial to the centre of the post, indicating that the post-cam contact
position translated medially during seiza-sitting, but not proximally.
Collectively, the seiza-sitting position seems safe against component
dislocation, but the risks of posterior
Background. Over 10% of total hip arthroplasty (THA) surgeries performed in England and Wales are revision procedures. 1. Malorientation of the acetabular component in THA may contribute to premature failure due to mechanisms such as
Retrieved alumina-on-alumina hip joints frequently exhibit a localised region of high wear, commonly called ‘stripe wear’. This ‘stripe wear’ can be replicated in vitro by the introduction of micro-separation, where the joint contact shifts laterally reproducing
INTRODUCTION. Studies have suggested that there is a reduction in head-neck-ratio (HNR) associated with MoMHRA. A reduction in HNR at operation would decrease range of movement and increase impingement risk. Impingement could lead to 20
Reasons for failure of hip resurfacing arthroplasty include femoral neck fracture, loosening, femoral head osteonecrosis, metal sensitivity or toxicity and component malpositioning. Patient factors that influence the outcome include prior surgery, body mass index, age and gender, with female patients having two and a half times greater risk of revision by 5 years than males . 1. –. 4. In 2008, the Australian National Joint Replacement Registry (ANJRR) reported poorer results with small sizes, whereby component sizes 44mm or less have a five times greater risk of revision than those 55mm or greater . 1. This finding is true for both males and females and after accounting for femoral head size, the effect of gender is eliminated. We explore the relationship between component size and the factors that may influence the survivorship of this procedure, resulting in higher revision rates with smaller components. These include femoral neck
We examined the relationship between the size
of the femoral cam in femoroacetabular impingement (FAI) and acetabular
pathomorphology to establish if pincer impingement exists in patients
with a femoral cam. CT scans of 37 symptomatic impinging hips with a femoral cam
were analysed in a three-dimensional study and were compared with
34 normal hips. The inclination and version of the acetabulum as
well as the acetabular rim angle and the bony acetabular coverage
were calculated. These measurements were correlated with the size
and shape of the femoral cams. While the size of the femoral cam varied characteristically,
the acetabular morphology of the two groups was similar in terms
of version (normal mean 23° (. sd. 7°); cam mean 22° (. sd. 9°)),
inclination (normal mean 57° (. sd. 5°); cam mean 56° (. sd. 5°)),
acetabular coverage (normal mean 41% (. sd. 5%); cam mean
42% (. sd. 4%)) and the mean acetabular rim angle (normal
mean 82° (. sd. 5°); cam mean 83° (. sd. 4°)). We found no correlation between acetabular morphology and the
severity of cam lesion and no evidence of either global or focal
over-coverage to support the diagnosis of ‘mixed’ FAI. The femoral
cam may provoke
Introduction: Although clinical results for the Metal-on-Metal (MoM) devices have been excellent, recently some concerns have been raised regarding the occurrence of periprosthetic soft tissue lesions (PSTL) in some patients with MoM devices. Clinical studies and retrieval analyses have shown that devices revised due to groin pain and PSTL generally have significantly higher wear that has been attributed to
Pseudotumour is a rare but important complication of metal-on-metal hip resurfacing that occurs much more commonly in women than in men. We examined the relationship between head-neck ratio (HNR) and pseudotumour formation in 18 resurfaced hips (18 patients) revised for pseudotumour and 42 asymptomatic control resurfaced hips (42 patients). Patients in whom pseudotumour formation had occurred had higher pre-operative HNR than the control patients (mean 1.37 (. sd. 0.10) vs mean 1.30 (. sd. 0.08) p = 0.001). At operation the patients with pseudotumours had a greater reduction in the size of their femoral heads (p = 0.035) and subsequently had greater neck narrowing (mean 10.1% (. sd. 7.2) vs mean 3.8% (. sd. 3.2) p <
0.001). No female patient with a pre-operative HNR ≤ 1.3 developed a pseudotumour. We suggest that reducing the size of the femoral head, made possible by a high pre-operative HNR, increases the risk of impingement and
INTRODUCTION. There is great potential for the use of computational tools within the design and test cycle for joint replacement devices. The increasing need for stratified treatments that are more relevant to specific patients, and implant testing under more realistic, less idealised, conditions, will progressively increase the pre-clinical experimental testing work load. If the outcomes of experimental tests can be predicted using low cost computational tools, then these tools can be embedded early in the design cycle, e.g. benchmarking various design concepts, optimising component geometrical features and virtually predicting factors affecting the implant performance. Rapid, predictive tools could also allow population-stratified scenario testing at an early design stage, resulting in devices which are better suited to a patient-specific approach to treatment. The aim of the current study was to demonstrate the ability of a rapid computational analysis tool to predict the behaviour of a total hip replacement (THR) device, specifically the risk of
The hip joint capsular ligaments (CL) passively restrain extreme range of motion (ROM) by wrapping around the native femoral head, and protect against impingement,
The hip joint capsule passively restrains extreme range of motion protecting against impingement, dislocation and possibly
Background. The hip joint capsular ligaments passively restrain extreme range of motion (ROM), protecting the native hip against impingement, subluxation,
We measured the contact areas and contact stresses at the post-cam mechanism of a posterior-stabilised total knee arthroplasty when a posterior force of 500 N was applied to the Kirschner Performance, Scorpio Superflex, NexGen LPS Flex Fixed, and NexGen LPS Flex Mobile knee systems. Measurements were made at 90°, 120°, and 150° of flexion both in neutral rotation and 10° of internal rotation of the tibial component. Peak contact stresses at 90°, 120°, and 150° were 24.0, 33.9, and 28.8 MPa, respectively, for the Kirschner; 26.0, 32.4, and 22.1 MPa, respectively, for the Scorpio; and 34.1, 31.5, and 32.5 MPa, respectively, for the NexGen LPS Flex Fixed. With an internally rotated tibia, the contact stress increased significantly with all the fixed-bearing arthroplasties but not with the NexGen LPS Flex Mobile arthroplasty. The post-cam design should be modified in order to provide a larger contact area whilst avoiding any impingement and
Introduction. The number of young and more active patients requiring total knee replacement (TKR) is increasing. Preclinical evaluation and understanding the long-term failure of TKR is therefore important. Preclinical wear simulation of TKR is usually performed according to the International Standards Organization (ISO) recommendations. Two international standards for preclinical wear simulation of TKRs have been developed so that the anterior-posterior (AP) translation and internal-external (IE) rotation can be driven in either force or displacement control. However, the effects of using different control regimes on the kinematics and wear of the same TKR have not been investigated. The current study investigated the kinematics, contact mechanics and wear performance of a TKR when running under ISO force and displacement control standards using an experimentally validated computational model. Materials/Methods. Three different ISO control standards were investigated using a size C Sigma curved TKR (DePuy, UK), with moderately cross-linked UHMWPE curved inserts; ISO-14243-3-2004, ISO-14243-3-2014 and ISO- 14243-1-2009. Axial force and flexion-extension angle are common for the three standards. AP and IE motions are displacement controlled in ISO-14243-3-2004 and ISO-14243-3-2014, with the only difference being a reversal of AP polarity between the two standards, and are force controlled in ISO-14243-1-2009. The test setup and soft tissue constraints were defined in accordance with ISO recommendations. The wear model was based on the modification of Archard's law where the wear volume is defined as a function of contact area, sliding distance, cross-shear and contact stress. The simulation framework has been independently validated against experimental wear rates under three different standard and highly demanding daily activities (Abdelgaied et al. 2018). Results. Reversing AP in the displacement control ISO-2014, compared to ISO-2004, resulted in high contact stresses of more than 70 MPa in the posterior direction. The predicted AP and IE from the force control ISO-2009 were in different directions and magnitudes to ISO-2014 AP and IE. The predicted wear rates were 1.8, 2.0, and 5.5 [mm. 3. /mc] for ISO-14243-3-2004, ISO-14243-3-2014 and ISO-14243-1-2009 respectively. Discussion. Reversing AP in the displacement control ISO-2014, without revising the femoral centre of rotation, resulted in high stress
Background. Trust in the validity of a measurement tool is critical to its function in both clinical and educational settings. Acetabular cup malposition within total hip arthroplasty (THA) can lead to increased dislocation rates, impingement and increased wear as a result of
Background. As the number of ceramic THR bearings used worldwide is increasing, the number of implants that experience off-normal working conditions, e.g.
Ceramic-on-ceramic bearings provide a solution to the osteolysis seen with traditional metal-on-polyethylene bearings. Sporadic reports of ceramic breakage and squeaking concern some surgeons and this bearing combination can show in vivo signs of
Background. Fretting at modular junctions is thought to be a ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to increased contact stresses and micromotions at the taper interface. We adopted a finite element approach to model the head-taper junction, to analyse the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants, to demonstrate the importance of a good assembly during surgery. Methods. Models of the Bimetric taper and adaptor were created, with elastic-plastic material properties based on material tests with the actual implant alloy. FE contact conditions were validated against push-on and pull-off experiments. The models were loaded according to ISO 7206-4 and −6, after being assembled at 2-4-15kN, both axially and at a 30° angle. Average micromotions and contact pressures were analysed, and a wear score was calculated based on the contact pressures and micromotions. Results. The average contact pressure decreased when a higher assembly force was used, with loads being distributed over a larger contact area, but increased when tested at a 30° angle. Average micromotions reduced with a higher assembly load, except when assembled at a 30° angle. The wear score decreased with increasing assembly force, when applied perpendicularly, while when assembled at a 30° angle, the wear score did not reduce with assembly force. Conclusions. The location and patterns of micromotions were consistent with retrieved tapers and those generated in in-vitro test models. Increased impaction loads reduced the average amount of micromotion and fretting. We intend to apply more complex loading regimes in future analyses, enabling to study phenomena such as
Metal-on-metal (MOM) hip arthroplasty has been associated with a variety of new failure modes that may be unfamiliar to surgeons who traditionally perform metal-on-polyethylene THR. These failure modes include adverse local tissue reaction to metal debris, hypersensitivity to metal debris, accelerated wear/metallosis, pseudotumours, and corrosion. A significant number of patients with metal-on-metal hip arthroplasty may present to surgeons for routine followup, concern over their implant, or frank clinical problems. A common issue with MOM hip arthroplasty that can lead to accelerated wear and failure is implant malposition. Malposition of a hard-on-hard bearing can lead to
Lewinnek's safe zone recommendation to minimise dislocations was a target of 5–25° for anteversion angle and 30–50° for inclination angle. Subsequently, it was demonstrated that mal-positioning of the acetabular cup can also lead to
Hip arthroplasty surgeons have various bearing choices to make on behalf of their patients. We make those choices based on our knowledge of pre-clinical wear testing data and the outcome of clinical and radiological follow-up studies. The initial use of conventional polyethylene revealed limitations in its use in younger patients. Modern highly crosslinked polyethylene is a vastly improved bearing surface that means less wear and its consequences. Despite this, registry data still suggests that loosening, lysis and dislocation are problematic causes of implant failure. The functional success of hip replacement surgery, the ageing population and younger patients requesting arthroplasty means we should predict ongoing issues consequent to wear related events even with the newer polyethylenes. Ceramic-on-ceramic bearings surfaces have a long history of successful clinical use. The benefits of ceramic bearings are its superior wear characteristics, the minimal biological response to the ceramic wear products and the ability of ceramics to be offered in larger head sizes. Its limitations have been reports of fracture and squeaking. Fourth generation ceramic articulations have reduced the fracture incidence. Squeaking has been reported to occur in 3% to 20% in different series but revision for squeaking is extremely, low suggesting it is not a significant clinical problem.
Squeaking in ceramic on ceramic bearing total hip arthroplasty is well documented but its aetiology is poorly understood. In this study we have undertaken an acoustic analysis of the squeaking sound recorded from 31 ceramic on ceramic bearing hips. The frequencies of these sounds were compared with in vitro acoustic analysis of the component parts of the total hip implant. Analysis of the sounds produced by squeaking hip replacements and comparison of the frequencies of these sounds with the natural frequency of the component parts of the hip replacements indicates that the squeaking sound is due to a friction driven forced vibration resulting in resonance of one or both of the metal components of the implant. Finite element analysis of
Introduction. Malpositioning of the acetabular cup during total hip arthroplasty increases the risk of dislocation,
A standard is defined as something established by authority, custom, or general consent. Clearly that does not exist for ceramic on ceramic total hip replacement. A better question is: Is there any indication for a ceramic on ceramic total hip. The answer to that question should when possible be based on clinical outcome data including the value added (or not) with this more expansive technology. Ceramic on ceramic has been popularised based on its low wear. Is this clinically relevant? Probably not, based on currently available data. Both metal on highly crosslinked polyethylene and ceramic on highly crosslinked polyethylene have very low clinically documented wear rates with excellent outcomes in multiple studies. In addition, ceramic on ceramic bearings are more sensitive to implant position. Whereas polyethylene may tolerated